Optical integrator rods are well known components used primarily in illumination systems for electronic projectors. An optical integrator rod is a hollow, or solid internally reflective "light pipe" which uses multiple reflections of a focused light source to obtain homogenization of round or irregular patterns of illumination and convert them into a uniform rectangular pattern. This pattern can be imaged onto a panel such as an LCD (Liquid Crystal Display) or DMD (Digital Micromirror Device) by a relay lens system and then projected to a screen. Thus, the optical integrator rod is used to improve uniformity and efficiently match the aspect ratio of the illumination source to the panel.
There are two basic types of reflective integrators: a "tunnel" type made of four mirrors, and a solid glass integrator or "solid rod integrator". This latter type is more efficient than the former since it works on lossless multiple reflections using TIR (the Total Internal Reflection) of the glass rod.
As a practical measure adopted to improve handling and reduce chips in the glass, opticians normally require a chamfer on the sharp edges of the glass rod. This chamfer (or the micro chips that result if the chamfer is absent) are imaged onto the panel and may show up as defects on the edges of the final image. To prevent this, the state of the art is to either over fill the panel or provide a thin output aperture plate over the end of the rod that is smaller than the glass. This precision plate guarantees dimensional accuracy, and sharp comers, but because it masks the defects and chamfers, it is necessarily smaller than the output face, and therefore restricts some of the illumination. This figure often amounts to about 10% of the useable light.
In order to improve efficiency and brightness, prior art optical integrator rods require an output face that presents a clear, sharp and unobstructed illumination to be imaged onto the panel by the relay lens. Because the focus of the relay lens must be sharp at the aperture for efficiency, it is also often sharp enough to pick up dust and defects at the focal point (e.g. glass defects and particles on the glass output face). A common solution to this problem is to move the aperture plate out a small distance, in order to ensure that the depth of focus of the lens does not focus the dust or defects onto the panel and the projection screen. However, this solution further exacerbates the problem of decreased efficiency and light output resulting from use of a precision aperture.